This invention relates generally to food freezing and also to defined refrigerant mixtures for generating refrigeration therefor.
Ammonia has long been used as the refrigerant for commercial food freezing because of its low cost. Generating refrigeration is an energy intensive process and, as energy costs continue to rise, it is desirable to have a refrigeration system which can provide comparable refrigeration for food freezing as can an ammonia system but with lower unit energy costs.
In addition to high power requirements, ammonia refrigeration systems have high capital costs and require significant physical space. It is desirable to have a refrigeration system for food freezing which has lower capital costs and requires less physical space than does a comparable ammonia refrigeration system.
Accordingly it is an object of this invention to provide a food freezing system which employs refrigeration generated using a system which has advantages over conventional ammonia refrigeration systems.
It is another object of this invention to provide a refrigerant mixture which can generate refrigeration for use in food freezing with an advantage over refrigeration generated from ammonia.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for freezing food comprising:
(A) compressing a refrigerant mixture comprising ammonia and at least one other component from the group consisting of hydrofluorocarbons and fluoroethers;
(B) cooling the compressed refrigerant mixture and expanding the cooled compressed refrigerant mixture to generate refrigeration;
(C) providing refrigeration from the expanded refrigerant mixture to food for freezing said food; and
(D) warming the expanded refrigerant mixture to effect at least in part the said cooling of the compressed refrigerant mixture.
Another aspect of the invention is:
A refrigerant mixture for generating refrigeration for use for freezing food, said refrigerant mixture comprising ammonia and at least one other component from the group consisting of hydrofluorocarbons and fluoroethers.
As used herein the term xe2x80x9cfoodxe2x80x9d means material intended for human or animal consumption and includes pharmaceuticals and other biological or organic materials.
As used herein the term xe2x80x9cfreezingxe2x80x9d means to provide refrigeration to food at a temperature of 260 K or less. Freezing includes chilling food, converting food to a frozen state, and/or maintaining food in a frozen or chilled state.
As used herein the term xe2x80x9cdirect heat transferxe2x80x9d means the passing of refrigeration from a refrigerant mixture to food with contact of the refrigerant mixture with the food.
As used herein the term xe2x80x9cindirect heat transferxe2x80x9d means the passing of refrigeration from a refrigerant mixture to food without contact of the refrigerant mixture with the food.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cexpansionxe2x80x9d means to effect a reduction in pressure.
As used herein the term xe2x80x9chydrofluorocarbonxe2x80x9d means a species whose molecular formula has only carbon and fluorine atoms, or a species whose molecular formula has only carbon, fluorine and hydrogen atoms.
As used herein the term xe2x80x9cfluoroetherxe2x80x9d means a species whose molecular formula has only carbon, fluorine and oxygen atoms, or a species whose molecular formula has only carbon, fluorine, oxygen and hydrogen atoms.
As used herein the term xe2x80x9cvariable load refrigerantxe2x80x9d means a refrigerant mixture having components in proportions such that the liquid phase of its components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the practice of this invention the temperature differences between the bubble point and the dew point for a variable load refrigerant generally is at least 5xc2x0 K.